Beomaster 4400 Type 2419: Final Reassembly and some final restoration tasks

This has been a marathon of a Beomaster 4400 restoration. Every time I thought I was ready for the home stretch some new problem would pop up.

With the testing out of the way this Beomaster has been playing constantly without any issues what-so-ever. So it is finally time to wrap this project up. Of course there were a couple of final repairs I had to make for this project to be complete.

The first was a known issue regarding the lenses for the slide controls. The old lenses were badly yellowed and foggy. I had already ordered a replacement set from Martin Olsen at Beoparts.

You can see how dark the background is in the picture above through the original lenses. The replacement lenses show what they should look like.

Reassembly of these components is a little tricky. The metal parts are very thin and probably had some special tool to mount them on the plastic slider at the factory. As such I found it very difficult to reattach them without any metal tabs breaking off. I ended up enlisting the aid of some very thin, double-sided tape (the kind used in modern cell phones) to put them back together.

The next issue was deterioration of the Beomaster 4400 cabinet feet. Almost all of the Beomaster 4400 units I have seen have feet that look like these.

You can see that there is also an accompanying rust problem.

This is the only part of the Beomaster cabinet that has any rust so I think the problem starts with the mounting screws of the feet.

I removed the old feet, sanded the rusty spots away, then spray painted the base plate (both inside and out).  I didn't want to lose the original wording and graphics on the cabinet base so I taped them off.

The rust is gone so I moved on to attaching the new feet.

The new feet have metal sleeves for the attachment screws so the screws don't compress the rubber as they are tightened. I threw the old feet and old screws away and used new mounting screws for the new feet.

The third and last issue I had to deal with was a broken FM tuning dial catch for the FM tuning slider.
All of these Beomaster 4400 units have a hard, brittle piece of glue that attaches the FM tuning slider to the tuning cord.

If you are careful with it the hardened piece of glue will remain on the cord and can be reused.
In this case it was too brittle and broke off.

There is not enough there to fit into the FM tuning dial catch.

The broken catch is always a blob of glue so I think the factory determined the position of the catch, set the tuning dial fork there and glued them together.  Whatever the type of glue they used was it does not bond to the slide control fork so it can be removed for service.

Over time however, those glue pieces break.

Looking for a solution that does not involve any permanent gluing to the slider fork I came up with using a small nylon washer and some epoxy to build me a new catch.

I marked either side of the tuning cord with a red marker before I removed that last remnants of the old glue piece.  That gives me the location for my new catch.

I used JB Weld fast drying, dark gray epoxy so I could easily see it.
I ended up having to cut some of the bottom part off because the catch was a little too big.
Note that this task is really something that should be done prior to having reassembled the Beomaster.
At this point though, I did not want to go through a whole disassemble and reassemble operation.

In the end my makeshift catch does a good job.

It fits into the tuning slider fork and the FM tuning slider operates the main FM tuning great.

Finally I could finish the reassembly of the Beomaster 4400 and get on with the best part...some listening tests.

Beomaster 4400 Type 2419: Checking the amplifier right and left channels

Before I finish reassembling this Beomaster 4400 receiver I made a few amplifier measurements to make sure the left and right channels are close to each other in their audio performance.

My testing methods cannot be the same as what Bang & Olufsen used back in the seventies so I am not looking to hit those same performance measurement values. The goal of my performance tests are to make sure the left and right channels perform the same...or at least very close to each other and that they are similar to other Beomaster 4400 units that have come across my workbench.. If one channel is way off the mark from the other on the same test then I have to figure there is something wrong.

The tests I like to use in comparing the channels are a Total Harmonic Distortion (THD) test on the output amplifier sections and the preamplifier sections. For that I use a QuantAsylum A401 Audio Analyzer to generate a 1Vrms sine wave test signal at 1KHz. That signal goes into the Beomaster 4400 Tape 1 source input. I measure the output at the preamplifier outputs then again at the output amplifier outputs (across an 8Ω dummy speaker load). It is actually an 8.08Ω load as I use a 0.08Ω series resistor as a sense load to make the measurements with the QA401 analyzer.

Here is the Beomaster 4400 connected up for testing.

The distortion measurements through the preamplifier were very good as expected.

So were the power amplifier outputs.

The frequency response measurements were also good. These tests are made using a frequency response plugin that is part of the QA401 Audio Analyzer. It executes a series of pulses at different frequencies and measures the output. The stimulus is still Tape 1 and the output is measured across the 0.08Ω dummy speaker load. When the test is complete the QA401 plots the output.

The end points (20Hz and 20KHz) are in the 1.0dB to 1.8dB range of the flat line which is pretty typical with this test setup. Both channels measure the same.

Satisfied with the electrical work so far, I will continue on with reassembling the Beomaster 4400 now and then some functional testing with all of the source inputs and listening tests of course.  Those are the most enjoyable tests to perform :-).

Beomaster 4400 Type 2419: Getting the FM tuner working

Power is good on this Beomaster 4400 now.  I have tested the Tape 1 and Tape 2 source inputs.  Now I can work on reinstalling the FM boards.

The first thing I will do is check if the FM boards have any power to ground short circuits. There were two traces burned up on the main board (PCB5) that involve ground and the +15VDC regulator. I am concerned those are related to the FM boards so I will test them by applying DC power to them via a bench power supply that I can regulate the current to. That way I won't let anything burn up.

First is the Stereo - Decoder board (PCB3).

No problem there.
I will move on to the IF and Tuner boards (PCB2 and PCB1 respectively).
PCB2 has both +15 VDC and +35 VDC.  I am testing with a dual 30 VDC bench supply so I will only do 30 VDC in place of the +35 VDC.

Great! No apparent power problems on the FM boards. I can reinstall them and give them a try.

The result...No FM at all from the Beomaster 4400.
Like most of the other issues with this Beomaster the problem came down to another broken wire.
Actually two wire issues with the FM tuner.
A ground wire from the main board - PCB5 to PCB6, a board on the switch rail, came loose.
Unfortunately the reattachment point on PCB5 is underneath the overhang of PCB6.  I am in no mood to disassemble the front panel to reconnect this wire.

Instead...I rewired the ground wire from the bottom side of the Beomaster.

Restoring that ground got all six of the FM preset tuning pots working again. The large, main tuning dial however was still not working.

The low side of the FM tuning pots for the six presets and the large tuning dial are supposed to tie together and connect to a leg of the 6R1 2.5KΩ trimmer. In addition there is an FM tuning voltage adjustment in the service manual to use 6R1 to set that common node to 4.6V.

I discovered that the connection of the six preset tuning pots and their connection to the 6R1 trimmer resistor did not include the main FM dial tuning pot. That trace must have a break in it but I could not see it.

As with the ground wire issue this problem would require another disassembly of the front panel. I did not want to do that so I used a jumper wire to fix the broken connection.

Now that the missing wires were fixed I could make the FM tuner upper and lower voltage adjustments per the service manual.

First the upper tuning voltage.  It is made with the main tuning dial all the way to the right.

That is followed by the lower tuning voltage adjustment. It is performed with the main tuning dial all the way to the left.

Finally, all of the FM tuning dials work....as do the signal strength and stereo indicator lamps.

Beomaster 4400 Type 2419: Reassembly and testing again (UPDATED)

I am pretty sure this has been one of the most difficult Bang & Olufsen restorations I have encountered.  Cleaning, recapping and adjusting a Beomaster 4400 receiver is not usually this difficult. The reason for that is I never had to dive in and disassemble the front panel. Unfortunately the power on/off switch on this one made it necessary for this project.

One big lesson I am taking from this project does involve the front panel and all of its related components. I started on the front panel by removing the minimal amount of things to get to the switch. That sounded good at the time but in hindsight the better approach (and the one I will use from now on) is to bite the bullet and disassemble everything from the front panel. Unobstructed access to the parts are the most important thing.

Had I done that from the outset I probably wouldn't have run into this situation...

It was time to re-install the rebuilt power on/off switch to the Beomaster 4400 switching rail.
The mounting tabs for the switch on the original switching rail were all but gone.
The tab on an unused switch mount is shown in the green circle. That is what the tab should look like.

I gave it a go anyway to see what it would take to mount the switch on the original switch panel.
NOT SO GOOD.  Obviously this is not Beolovely and unacceptable.

I had another switching rail from a spare parts Beomaster 4400 that the replacement power on/off switch came out of.  It still had serviceable mounting tabs.

Here is what I mean about complete disassembly of the front panel.
The switch panel assembly is removed in the photo above but for full access and working room in remounting the power on/off switch, the circuit board (and flexible circuit assemblies) should be removed.

With the switch remounted I reinstalled the circuit board (PCB6). Note that in the photo below I also desoldered the flexible circuit from the FM preset assembly.  This is important to do because the preset assembly is bulky and heavy. Leaving it attached makes it very risky to cause the flex circuit to crack and break. I have seen cases of that. So play it safe and just desolder the flex circuit from the preset assembly.

While PCB6 and the flex circuit were separated I took the opportunity to replace the 6R1 2.5KΩ trimmer. If the trimmer needed to be replaced later I would have to completely disassemble all of this again and I really want to avoid that. So to be safe I replaced it with a new Bourns trimmer.

Another thing to take care of for future insurance is the small, red FM Stereo indicator lamp. It is an LED that has been glued to the Beomaster 4400 front panel.

I investigated removing it but I couldn't figure out how without breaking the LED.

So I reconnected wires to the lamp with a small, two-pin connector for ease in removing the front panel. I also tested the LED.

That appeared to work but when working on the front panel reassembly one of the LED wires broke off again.

I reworked the wire attachments to be more secure and used a dab of epoxy on each wire to fix it to the panel as a strain relief for the leads to the LED.

In the process I didn't notice that I got the wire colors reversed where they attach to the LED. Luckily I have the 2-pin connector I had added earlier so I can just take care of the polarity there.

Continuing on with the front panel reassembly I reconnected the components.
I didn't break out the individual steps in photos (sorry) but I did find that mounting the switch rail to the toggle switch actuators and front panel is really, really difficult to do if the actuator assembly is already attached to the front panel.

I was successful by first attaching the actuator assembly to the switching rail. This allowed me to properly set the position of the actuators.

After that mini-assembly I was able to fit the switching rail with the actuators pretty easily into the front panel.

Next up was the task of resoldering all of the wires I had to remove as part of the disassembly.

Here are a couple of photos of the reattachment of the flexible circuit to the FM Preset assembly and the remounting of the main FM tuning dial.

Finally the new power on/off switch can be hooked up to the Beomaster 4400 and I could try another power test.

I applied power with my variac and dim bulb tester in the circuit for safety.
The first thing I checked was the +15 VDC regulator as that was part of the earlier repair where there were burned up ground traces on PCB5.
I also still have the FM boards removed from the Beomaster. Because they were involved with the burned ground traces I need to check them out separately before putting them back into this Beomaster.

Another quick check was made on the idle current for both channels in the output amplifiers.  They did require some adjustment so I performed those and the Beomaster 4400 was ready for a listening test.

Like before I used a pair of headphones and an iPod Nano connected to the Tape 1 input.

Success finally.  The new power switch operates perfectly and I have nice music playing through the Tape 1 source.

With this Beomaster 4400 unit though, it would not be in character for everything to work perfectly.

A new issue has popped up. I had to use the Linear switch to get sound in both channels. With the Linear switch deselected the left channel drops out.

The Linear switch is an option to bypass the Treble and Bass tone control section of the Beomaster 4400 preamp. So either the left channel is not making it through the tone controls or there is a problem with the Linear switch.

I was hoping it is just a wire that isn't mating well (maybe broke off during the front panel reassembly)

Sure enough, a broken wire to the switch.

I resoldered the broken wire and now the normal stereo selection works.

Now that problem is solved and I can return to the FM boards on this unit.